1. Field of the Invention
The present invention relates to signal processing and, in particular, to computer-implemented processes and apparatuses for processing video signals received from a digital video caldera.
2. Description of the Related Art
This invention relates to computer processing of video signals received from a video source such as a video camera. In current usage, video cameras produce analog video signals which are sent to a computer via a coaxial ("coax") cable. Often an I.sup.2 C interface is provided to control the camera's registers and to supply power, for example, for small video-conferencing cameras. The I.sup.2 C interface provides a standard for controlling video components that require, for example, 100 to 400 kilobits per second of instructions.
Referring now to FIG. 1, there is shown a prior an analog video camera system 100. As illustrated camera system 100 comprises an analog video camera 101 and a computer 102, which are interconnected via Coax+I.sup.2 C connection 103. The dotted line surrounding connection 103 represents shielding. The coax portion of connection 103 supplies analog video voltage signals to computer 102/ for analog-to-digital conversion and further processing, and the I.sup.2 C portion of connection 103 provides for a relatively low rate of digital control signals transmitted from computer 103 to camera 101.
Current analog video cameras usually perform digital signal processing to provide high quality image processing of the video signal. In one current usage, the analog video camera has a digital processing system ("DSP") subsystem to perform sophisticated image processing, as shown in FIG. 2. Referring now to FIG. 2, there are shown in further detail the components of camera 101 of prior art system 100 of FIG. 1. As illustrated, analog camera 101 comprises a lens 110, physically located near a charged-coupled device ("CCD") 111. An image is focused on CCD 111 by lens 110. CCD 111 provides analog voltage signals corresponding to the image, which are convened to digital signals by analog-to-digital converter ("A/D") 112. These digital signals are further processed by DSP 113, and reconverted to analog signals again by D/A 114. These processed analog video signals are then transmitted as "video out," as illustrated, to a video processor such as computer 102. Video camera 101 also comprises timing/voltage controller 115, read-only memory ("ROM") and random-access memory ("RAM") 116, and controller 117, which receives I.sup.2 C standard control signals from computer 102. Controller 117 is used, for example to enable automatic gain control, shutter speed automatic light balance, and the like.
Computer 102 typically comprises various hardware modules which convert the analog voltage signal into digital pixels arrayed in main memory, as illustrated in FIG. 3. Referring now to FIG. 3, there are shown in further detail the components of computer 102 of prior art system 100 of FIG. 1. Computer 102 receives the analog video signals produced by video camera 101, as signals "video in" at a convenient terminal at personal computer ("PC") interface 121. These analog video voltage signals are converted to digital signals by A/D 122, decoded, scaled, and subsampled by decode 123. scale 125, and color subsample 126. These subsampled YUV signals may then be stored in main memory 129 via peripheral component interconnect ("PCI") interface 127 and PCI bus 128. As shown in main memory 129, the YUV digital signals, which represent planar pixel data, are typically stored in subsampled format such as the illustrated YUV 4:1:1 tiermat, in which every (4.times.4) block of pixels of the Y component plane corresponds to a single pixel in the U component plane and a single pixel in the V component plane.
Unfortunately, such a video camera and video processing system which is based in this manner upon analog signals requires a relatively large number of chips, components, and processing steps, which necessitates tradeoffs between cost and video quality. Such prior art systems thus require either relatively large expense, in terms of cost and complexity, for good quality video, or result in much lower quality video if lower cost is a constraint. Further, instead of utilizing DSP 113, a lower cost solution might have a dedicated application-specific integrated circuit ("ASIC"), but this solution is less powerful and less flexible than the use of DSPs. In addition, because the signals are convened from analog to digital and back to analog, and because the signals are transmitted in analog form, this method is prone to error.
There is thus a need for improved methods and apparatuses for processing video camera signals.